Phase modulation



I M A LEONRUBIN March 2,1948. ,RUB 2,437,047

PHASE MODULATION Filed Dec. 25, 1943 3 Sheets-Sheet .ZZZQ. .Z-

PHASE /10 I SHIFTER MAIN k IN VEN TOR.

A1 I ORNEY Mar ch 2, 194a.

1.. RUBIN PHASE MODULATION Filed Dec. 25,- 1943 3 Sheets-Sheet 2 MAIN OSCILLATOR B I MODULATOR fig. 6. all

4? PHASE 1 SHIFTER 10 I 12 MAW 3 LOAD I OSCILLATOR iE0 MODULATOR if; I- I MPEMCE I l T; PHASE 116' a v SHIFTER 2 15 V2 LEUNRUBIN INVENTOR.

BY I 1.

AT T ORNL'Y March 2, 1948. 1.. RUBIN 2,437,047

' PHASE MODULATION Filed Dec. 23, 1945 3 Sheets-Sheet 3 POWER AMPLIFIER I Ji' FREQUENCY MULTIPLIER MAIN kja LOAD FREQUENCY OSCILLAT0R1 MODULATOR IMPEDANCE MULTIPLIER PHASE SHIFTER .ZZ I L n;

LEOZV RUBIN INVENTOR.

A TTORNEY Patented Mar. 2, 1948 PHASE MODULATION Leon Rubin, Buenos Aires, Argentina, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 23, 1943, Serial No. 515,446 9 Claims. (Cl. 179171.5)

This invention relates to phase modulation and more particularly to an improved phase modulation circuit especiallyuseful for frequency modulation transmitters.

It is known that a phase modulated oscillation can be obtained by either combining the carrier wave in quadrature with theside bands or by linearly modulating in phase opposition the amplitudes of two oscillations having a given phase difference and by combining these amplitude modulated oscillations. In both systems, one extreme of the vector representing the resulting phase modulated oscillation in the corresponding vector diagrarn, slides along a straight line perpendicular to the vector representing the unmodulated oscillation during a complete modulation cycle, while in an ideal phase modulating circuit this phase modulated vector slides along an arc of a circle, drawn with said vector as radius.

Consequently, in these systems, the relation between phase angle and amplitude of the modulating potential cannot be linear, the admissible tolerance in distortion usually limiting the phase angleto a maximum value of approximately,

I have now found that if the amplitude of two oscillations having a phase difference smaller than 1r radians is non-linearly modulated in phase opposition in accordance with the amplitude variations of an intelligence oscillation, the vector sum of these oscillations will represent a phase modulated oscillation which, for some optimum value of phase angle betweenthese amplitude modulated oscillations, will closely approach the characteristics of an ideal phase modulating circuit. In fact, the vector representing the phase modulated oscillation obtained will alternatively slide with its end along two lines which, forming some angle with a straight line perpendicular to the vector representing the resulting oscillation in the absence of modulation, constitute the complementary lines of the corresponding vector diagram, so that these two lines in View of their inclination, may be regarded to represent the corresponding arc of the ideal phase modulating circuit in first approximation.

It is therefore one oi. the main objects of the present invention to provide a phase modulating system wherein the relation between the amplitude of the modulating potential and phase angle of the modulated high-frequency oscillation will be linear over a wide range of phase angle varia- T tions.

A further object of the present invention is toprovide a phase modulating system which, while being of simple circuit layout and including a minimum of circuit elements allows of a maximum variation in the phase angle.

Another object of the present invention is to provide a transmitter in which the number of frequency multiplier stages necessary to obtain the modulation index required, will be less as compared with the known frequency modulation systems. 7

The above and further objects and advantages of the present invention will become more ap-.

parent from the following detailed description taken with reference to the accompanying drawings forming part of this specification and wherein:

Fig. 1 is a block diagram, schematically showing one embodiment of the present invention.

Figs. 2A to 5 are explanatory diagrams relating to the operation of the phase modulation system shown in Fig. 1.

Fig. 6 is a circuit diagram of the phase modulation system according to Fig. 1.

Fig. 7 illustrates a modification of the circuit shown in Figs. 1 and 6.

Fig. 8 is an explanatory vector diagram relating to the operation of the phase modulation system shown in Fig. '7. V 7

Fig. 9,shows still another modification of the phase modulation system shown in Figs. 1 and 6.

Fig. 10 is an explanatory vector diagram relating to the operation of the system shown in Fig. 9, and finally I Fig. 11 schematically illustrates-a transmitter using the phase modulating circuit according to one embodiment of the present invention.

The same reference characters are used to indicate like or corresponding parts or elements throughout the drawings.

Referring now to Fig. 1, it may be seen that oscillator l0, generating a main oscillation E0, is coupled through phase shifters P1 and P2 to control grids gc of thermionic tubes V1 and V2, respectively, the anode circuits of which are connected in parallel to a common load impedance Z, connected to the positive pole H of a direct current supply not shown in the drawing. Control grids g'e of these tubes, provided with grid leak resistances l2, are coupled in push-pull by means of coupling condensers l3 to a modulator I4 constituting a source of modulating potential Vm. I

As can be observed in the vector diagram shown in Fig. 2 A, phase shifters P1 and P2 are designed so that; partial oscillations e1 and c2 derived from main oscillation E and amplified by tubes V1 and V2 have their phase shifted +0 and -0 degrees, respectively, from the phase of said main oscillation E0, the sum of these angles 0 being always smaller than 1r radians. Consequently, in the absence of modulation the output oscillation E', appearing at the output terminals l5 and it of the phase modulation system and developed across common load impedance Z, will represent the vectorial sum of partial oscillations er and c2 and will be in phase with main oscillation E0.

The control circuits of tubes V1 and V2 including grids 9'0 and gc are designed to operate with grid current saturation during the positive half periods of the modulating potential Vm by utilizing very large resistances as grid leaks 12, the time constants of the combination of coupling condensers I3 and grid leak resistances l I being however, smaller than the periods of the highest modulation frequency. Hence assuming that the positive half wave of modulating oscillation Vm is present on control grid gc of tube V1, the amplitude of partial oscillation e1 generated by this v Vm.

tube across load impedance Z, will be maintained constant, while the amplitude of partial oscillation e2, generated by tube V2 across the same load impedance Z, will first decrease to a minimum value or to zero and then again increase to its maximum value in synchronism with the amplitude variations of the negative half wave of said modulating oscillation or potential Vm, as can be observed in the vector diagram shown in Fig. 213, where curves I1 and I8 illustrate the biasing potentials present at control grids g'c of tubes V1 and V2, respectively, while curves l9 and shown in Fig. 3 represent the high frequency current generated by these tubes across common load impedance Z. It is therefore evident that vector E in the diagram shown in Fig. 213, corresponding to the output oscillation appearing between terminals l5 and It of the phase modulation system according to the present invention, is equal to the vector sum of partial oscillation :21 which is maintained on its maximum amplitude and partial oscillation eg the amplitude of which is determined by the amplitude of modulating oscillation Vm which, in the vector diagram shown in Fig. 2B. is illustrated at some arbitrary time to. Output oscillation E thus has its phase shifted +p from the phase of oscillation Eu which is in phase with vector E representing the unmodulated output oscillation. Since the amplitude modulation of partial oscillations er and 62 is carried out in phase opposition or push-pull, it will be obvious that during a complete cycle of the modulating oscillation Vm, phase angle o of output oscillation E will vary from zero to :0 and that the extreme of vector E will slide along straight lines 2| and 22 which complete the vector diagram and which form the angles +oc and a, respectively, with straight line 23 perpendicular to vector E representing the unmodulated output oscillation E.

Lines 2! and 22, each forming partof the vector diagram, intersect circumference 24 of a circle drawn with E as a radius at two points and may be regarded as the first approximation of the arc included between these intersection points, so that the phase modulation characteristics of the system according to the present invention, reproduce more closely the operatingconditions in the ideal phase modulation circuit as the known phase modulation system wherein the extreme of vector E would slide along straight line 23. Therefore, it will be evident for those skilled in the art that the range over-which the relation between the amplitude of modulating oscillation or potential Vm and phase angle q) will be wider in the phase modulation system according to the present invention, than in the known phase modulation systems, and that for some optimum value of 0 this relation will be perfectly linear for all practical purposes.

The advantages of the novel phase modulation system can be fully appreciated in the graphs shown in Figures 4 and 5, the first showing curves 25 and 26, representing the relation between phase angle 1p and amplitude of modulating potential Curve 25 has been drawn for a phase difference 0 90", i. e.illustrating the operating conditions of the known phase modulation systems, while curve 26 has been drawn with 0= 60 as parameter, this value representing the optimum phase difference between main oscillation E0 and partial oscillations er and ea. As can be observed in Fig. 4, curves 25 and 25 illustrate in a drastic manner the limitations inherent to the known phase modulation systems in which a linear relation between the amplitude of modulating potential Vm and phase angle m can be obtained over a range of :30" only, while in the phase modulation system according to the present invention this relation is practically perfectly linear over a range of :60. Hence, frequency modulation systems, utilizing the phase modulation circuit according to the present invention, will require fewer frequency multiplier stages to obtain a given modulation index and consequently will represent not only a better technical but also a more economic solution of the problem to produce phase. or frequency modulated oscillations.

In Fig. 5 curves 2! and 28 illustrate the relation between the amplitude of the phase modulated oscillationE and phase angle (p, the curves being drawn with 0=90 and 0= 60 as parameters. It is well known in the art that owing to the particular organization of the known phase modulation systems, the phase. modulation of the output oscillation is inevitably accompanied by an amplitude modulation and that this amplitude modulation constitutes one of the main drawbacks of the known systems in which amplitude limiter stages have to be used in orderto obtain an output oscillation modulated in phase. only. Curve 2] quite clearly illustrates these unfavourable op erating conditions of the known phase modulation systems which in fact can be regarded as a phase modulation system wherein phase differ ence 0 between partial oscillation e1 and 62 is'equal to zero, and it can be'seen that for a phase angle of 70 the amplitude'of the phase modulated oscillation E has increased to three times its original amplitude. V

In contradistinction to the known phase modulation systems, the amplitude of phase modulated oscillation E remains practically constant over a range of phase angles from zero to 70 when the phase difference 0 between E and partial oscillations e1 and e2 is equal to the optimum value of 60, as illustrated by curve 28 shown in Fig. 5.

It will be understood that the advantages and improvements inherent to the phase modulation system according to the present invention are obtained in view of the fact that phase modulated output oscillation E is obtained as the vectorial sum of two partial oscillations c1 and c2 having a phase difference smaller than 1r radians and the amplitudes of which are non-linearly modulated or varied in phase opposition in accordance with the amplitude variationsof modulating potential Vm, so that the end'of vector E representing this output phase modulated oscillation in the corresponding vector diagram will slide along two straight lines 2| and 22 formingan angle equal to the phase difference between partial oscillations c1 and 6;.

In the schematic block diagram shown in Fig. l as well as in the circuit diagram in Fig. 6, representing one of the embodiments of the phase modulation system according to' the present invention, the non-linearity of the amplitude modulation of partial oscillations er and as is obtained by grid current saturation of thermionic tubes V1 and V2. However, this represents one of the many possible arrangements for non-linearly modulating partial oscillations er and c2 and a somewhat different circuit for this purpose will be described hereinafter.

As can be seen in the circuit diagram shown in Fig. 6, output terminals 29 and 30 of main oscillator in are connected to phase shifters P1 and P2 formed by the series connected condenser 3|, resistance 32 and condenser 33 and resistance 34, respectively. As can be seen in the drawing, resistance 32 and condenser 33 are connected to output terminal 29 of main oscillator it, while condenser 32 and resistance 34 are connected to the opposite terminal 30, thejunction points between the condensers and resistances of phase shifters P1 and P2 being coupled by means of coupling condensers I3 and conductors 35 and 36, respectively, to the control grids go of thermionic tubes V'1 and V2. Control grids gs of these tubes are connected, as already explained hereinabove, through grid leak resistances l2 to the ends of the secondary winding 31 of a modulation transformer T, the primary winding 38 of which is connected to modulator i l. The electrical mid-point of secondary winding 31 is connected together with the cathodes of said thermionic tubes V'1 and V2 to ground potential.

The circuit elements of phase shifters P1 and P2 are designed so that partial oscillations er and 62 applied to control grids go of tubes V1 and Vz have their phase shifted $0 from the phase of main oscillation E0 and, although in the circuit diagram shown in Fig. 6 these partial oscillations are applied to control grid gc together with modulating potential Vm, the operation of this circuit is similar to that shown in Fig. 1.

Thus the phase modulated oscillation E is obtained in the phase modulation system according to Figures 1 and 6 by combining two partial oscillations e1 and e2 having a phase difierence smaller than 180 and by alternatively maintaining one of these partial oscillations at its maximum value, while decreasing the amplitude of the other partial oscillation to a minimum value and back to said maximum amplitude, so that vector E, representing the phase modulated oscillation in the corresponding vector diagram, will slide along two straight lines 2| and 22 forming an angle equal to the phase difference between said partial oscillations.

However, the same results may be obtained by vectorially combining an oscillation of constant amplitude and phase with two partial oscillations having their phase shifted :0 from the phase of this oscillation and by varying the amplitude of one of these partial oscillations from zero to a maximum value and back to zero, while substantially completely supressing the other partial oscillation, and vice-versa.

In the circuits representing the phase modulation system according to the the embodiments of smaller than 1r/2, and the schematic block dia- 7 gram shown in Fig. 7 illustrates a phase modulation system incorporating the abovementioned condition. The only difference between the circuit layout shown in Fig. 7 and that of Fig. 1 consists in that the anode circuits of thermionic tubes .V1 and V2 are connected in push-pullto load impedance Z", so as to compensate the smaller value of the original phase difference between partial oscillations e'1 and ez derived from main oscillation-Eo by means of phase shifters P"1 and P"2, respectively.

As already explained hereinbefore, in the system according to Fig. 1 the phase modulated output oscillation E is obtained by vectorially combining two partial oscillations c1 and 82 which are derived from main oscillation E by means of phase shifters P1 and P2 and which have a phase difierence +0 and 0 respectively with reference to said main oscillation, the amplitudes of these partial oscillations being non-linearly modulated in accordance with the amplitude variations of modulating potential Vm.

Now let us assume that phase shifters P"1 and P"2 are designed so that partial oscillations e1 and e'z have their phases shifted +0 and -0' degrees respectively, from the phase of main oscillation E0, as can be observed in the vector diagram shown in Fig. 8. In the phase modulation system according to Fig. 1, the phase relationship between partial oscillations c1 and ez applied to the control grids of tubes V1 and V2 and the amplitude modulated partial oscillations developed across common load impedance Z is not altered, since the anode circuits of both tubes are connected in parallel, so that the phase inversion of taking place in each tube, does not affect the phase difference between the partial oscillations.

However, in the circuit shown in Fig. 7 the anode circuits of tubes V1 and V2 are connected in push-pull. Hence, tube V1 may be regarded as operating in a Way similar to that of the circuit shown in Fig. 1, While tube V2 will generate across load impedance Z a partial oscillation e"z which will be 180 out of phase with respect to partial oscillation e'z applied to'control grid gs of this tube. Consequently, the phase modulated output oscillation E will be now formed as the vector sum of partial oscillation e'1 generated by tube V1 and partial oscillation e"2 generated by tube V2, and the vector diagram of Fig. 8 clearly shows that there is no difference between the results obtained with the circuit shown in Figs. 1 and 2. Consequently, in the phase modulation system according to Fig. 11, thermionic tube V2 operates not only as an amplitude modulator for partial oscillation e'z but also constitutes part of the phase shifter P2, so that the vectorially combined partial oscillations e'i and e2 have a phase difference smaller than 1r but larger than 1r/2.

It has been already explained hereinbefore that the basic idea of my invention consists therein that during modulation the end of the vector representing the phase modulated output oscillation is made to slide along two straight lines 2| and 22 representing the first approximation of an arc of the ideal phase modulation 7 circuit, this result being obtained by non-linearly modulating the amplitudes of partial oscillations er and c2 having a phase difference smaller than "In the circuits described hereinbefore, the nonlinear modulation has been achieved by varying the amplitude of partial oscillations 421 and ea or e'i and ez, during one half-period only of modulating oscillation Vm, the amplitude of these partial oscillations remaining unchanged during the other half-periods of Vm. However, I have found that if the amplitude of said partial oscillations is also varied during a portion of the half-period usually not utilized for modulation, a phase modulation system will be obtained which will reproduce Still better'theoperating conditions of the ideal phase modulation circuit, provided that the amplitude variation of e1 and ea or 6'1 and 6'2 will be maintained within certain limits during these half-periods.

The schematical block diagram shown in Fig. 9 illustrates a phase modulation system incorporating the aforementioned improvement, the cir-' cult differing from the circuit shown in Fig. 1 in that control grids gs of thermionic tubes V1 and V2 are connected to anodes a of a double diode V4, the common cathode is of which is connected to the movable arm of a potentiometer 44 connected in shunt across a direct current supply d5, the negative pole of which is coupled together with the cathode of tubes V1 and V2 to ground potential.

When cathodes 7c of diode tube V4 are connected to ground potential, the positive half-periods of modulating oscillation Vm will not aiTect the operation of tubes V1 and V2 which will remain conductive over the whole duration of these, halfperiods. The operation of the circuit shown in Fig. 9 will be similar to that of the circuit shown in Fig. 1. If, however, cathodes k of diode tube V4 are made positive by conveniently adjusting the movable arm of potentiometer 45, then the amplitude of partial oscillation c1 and c2 will also be varied during portions of the positive halfperiod of modulating oscillation Vm and will remain substantially constant during the remaining portion of these half-periods, the relationship between these portions being determined by the positive bias of cathode K of double diode V4.

As can be observed in the vector diagram shown in Fig. 10, vector E representing the phase modulated output oscillation obtained between the output terminals to and it of the circuit will first slide with its end along straight line'23 during the positive half-period d5 of modulating oscillation Vm, the distance between intersection point all of line 23 and vector E (representingoutput oscillation E in the absence of modulation) and points iii and ie on the same line, being determined by the amplitude of positive half periods iii of Vm. During the negative half-waves ll of Vm the end of vector E will slide along straight lines 55 and El interconnecting points its and 39 with points 52 and 53 respectively, the latter points corresponding to the ends of vector or and oz in the absence of modulation.

It will be understood that the combination of line 53, portion ie-t9 of straight line 23 and line ill constitutes a better approximation of arc 2 of the ideal phase modulation circuit than the combination of straight lines it and 22 obtained in the vector diagrams of the circuits described hereinbeiore. It will be also understood that by conveniently adjusting the amplitude of positive half-periods 4'6 of modulating oscillation Vin,

lines 55 and 51 can be made'to'oross the corresponding portions of are 24 at two points (as shown), thus obtaining a phase modulation systom the output characteristics of which will practically be equal to those of the ideal phase modulation circuit.

Fig. 11 illustrates the schematic block diagram of a transmitter incorporating a phase modulation system according to the present invention. As can be seen in the drawing, the novel phase modulator, designated by the general reference number is coupled by means of two frequency multiplier stages 55 and 56 to power amplifier 57 provided with antenna 58. Since the amplitude of the phase modulated output oscillation E present at the input of frequency multiplier stage 55 remains substantially constant throughout the whole range of phase variations, it is not necessary to use amplitude limiter stages between the phase modulator 54 and the other stages of the transmitter, Furthermore, the number of frequency multiplier stages can be kept at a minimum due to the wide range of phase angle variations which can be obtained in the phase modulation system according to the present invention.

While I have shown my phase modulation sys tern as utilizing phase shifters of the resistance capacitance type, it will be understood that the present invention is not limited to the use of such phase shifters. Obviously, other types of phase shifters can be used, since the primary object of these circuit elements is to derive from main oscillation E0 the partial oscillations c1 and 122 having some predetermined phase difference. Similarly, it will be apparent to on skilled in the art that my invention is by no means limited to the particular arrangements shown and described, but that many modifications may be made without departing from the scope of, the invention.

I claim:

l. The method of varying the phase of an electrical oscillation in accordance with the amplitude variations of a modulating potential, which comprises the steps of generating a main oscillation, deriving from said main oscillation two partial oscillations having a phase difference smaller than 1r radians, antiphasally varying the amplitudes of said partial oscillations in accordance with the amplitude variation of a predetermined portion of the period of said modulating potential, antiphasally maintaining the amplitudes of said partial oscillations substantially constant during the remaining portion of the period of said modulating potential, and vectorlally addlng, said non-linearly amplitude modulated partial oscillations to produce an electrical oscillation having a phase angle substantially proportional to the amplitude of said modulating potential.

2. The method of varying the phase of an electrical oscillation in ace-o dance with the amplitude variations of a modulating potential, which comprises the steps of generating a main electrical oscillation, deriving from said main oscillation two partial oscillations having a phase difierence smaller than 71' radians, antiphasally varying the amplitudes of said partial oscillations in accordance with the ampl ude variations of the halfperiods of one polarity of said modulating potential, antiphasally maintaining the amplitudes of said partial as at is substantially constant do? ng the half-periods of the other polarity of said modulating potential, and vectorially adding said non-linearly amplitude modulated partial oscillations to produce an electrical oscillation having a phase angle substantially.proportional to the amplitude of said modulating potential. 3. The method of varying the phase angle of an electrical oscillation, in accordance with the amplitude variations of a-modulatin-g potential, which comprises the steps of generating a main electrical oscillation, deriving from said main oscillation two partial oscillations of substantially equal amplitude and having a phase difierence smaller than 1r radians, antiphasally varying the amplitudes of said partial oscillations from a maximum to aminimum andback to said maximum value in accordance with the negative half.- periods of said modulating potential, antiphasally maintaining'the amplitudes of-said partial oscillations substantially constant during the positive half-periods of saidmodulating potential, and vectorially adding said non-linearly amplitude modulated partial oscillation to produce an electrical oscillation having a phase anglesubstantially proportional to the amplitude of said modu lating potential.

4. A phase odulation system comprising, means for generating a main electrical oscillation, means for deriving from said main oscillation two partial oscillations having a phase difference smaller than 1r radians, a source of a modulating potential, an amplitude modulator having a non-linear modulation characteristic connected to said partial oscillation deriving means and coupled tosaid source of modulating potential generating means to antiphasally vary the amplitudes of said partial oscillations in accordance with the amplitude variations of a predetermined portion of the period of said modulating potential and to antiphasally maintain the amplitudes of said partial oscillation substantially constant during the remaining portion of the period of said modulating potential, and means connected to said amplitude modulation means to vectorially add the amplitude modulated partial oscillations to produce an electrical oscillation having a phase angle substantiall proportional to the amplitude of said modulating potential. I

5. A phase modulation system comprising, mean for generating a main electrical oscillation, phase shifting means coupled to said main oscillation generating means to derive two partial oscillations" of substantially equal amplitude and having a phase difference smaller than 1r radians, a source of a modulating potential, two thermionic tubes each having a cathode, at least one control electrode and an anode, each of said control electrodes being coupled to one of said phase shifting means in an oscillation ampl ation arrangement, said control electrodes bein ,also coupled to said source of modulating potential in a push-pull arrangement, means to operate said control electrodes under grid current saturation circuit condition thereby to vary the amplitudes of said partial oscillations in phase opposition from a maximum value to a minimum and ack to a maximum value in accordance with the negative half-periods of said modulating potentia1 and to maintain the amplitudes of said partial oscillations substantially constant in phase opposition during the positive half-periods of said modulating potential, and a load impedance element connected in parallel with the anodes of said tubes for vectorially adding the amplitude modulated partial oscillations to produce an electrical oscillation having a phase angle substantially proportional to the amplitude of said modulating potential.

6.- Ajphase modulation system comprising, an oscillator for generating a main oscillation, two phase shifters connected after said oscillator to derive from said mainoscillation two partial oscillations of substantially equal amplitude and having a phase difference substantially equal to %1r radians, a source of a modulating potential, two thermionic tubes each having a cathode-a control electrode and an anode, the control grids of said thermionic tubes being coupled each to one of said phase shifters, a modulating transformer having a primary winding coupled to said modulating source and a secondarywinding having its electrical midpoint connected to the cathodes of said tubes, grid leakresistors interconnecting the ends of said secondary winding to the said control grids in a push-pull grid-current saturationv circuit arrangement, anda load impedance element connected in parallel to the anodes of said, tubes for vectorially adding the amplitude modulated partial oscillations toproduce an electrical oscillation having a phase angle substantially proportional to the a plitude of said modulatingpotential, V

7. A phase modulation system comprising, an oscillator for generating a main oscillation, two phase shifters coupled to said oscillator to derive from said main oscillation a first and a second partial oscillations of substantially equal amplitude and having a phase difierence smaller than 11- radians, a source of a modulating potential, two thermionic tubes each having a cathode, a first and a second control electrode and an anode, each of said first control electrodes being coupled to one of said phase shifters, while said second control electrodes are connected in push-pull to said source of modulating potential, each of said second control electrodes being returned to the cathode of the corresponding tube through a half-wave rectifier circuit and a source of direct voltage, to antiphasally vary the amplitudes of said artial oscillations during a portion greater than half of the period of said modulating potential, and to antiphasally maintain the amplitudes of said partial oscillations substantially constant during the remaining portion of the period of said modulating potential, and vectorial addition means constituted by a load impedance connected in parallel to the anodes of said tubes to produce an electrical oscillation having a phase angle substantially proportional to the amplitude of said modulating potential.

8. A phase modulation system comprising, an oscillator for generating a main oscillation, two phase shifters coupled to said oscillator to derive from said main oscillation two partial oscillations of substantially equal amplitude and having a phase difference smaller than 11' radians, a source of modulating potential, two thermionic tubes each having a cathode, a first and a second control electrode, and an anode, each of said first control electrodes being coupled to one of said phase shifters, means to antiphasally vary the amplitudes of said partial oscillations in accordance with the amplitude variations of the negative half-period and a variable part of the positive half-period of said modulating potential and to antiphasally maintain the amplitudes of said partial oscillations substantially constant during the remaining portion of the positive half-periods of said modulating potential, comprising means to couple said second control electrodes in pushpull to said source of modulating potential, two I rectifier tubes having their anodes each connected to one of said second control electrodes,

11 a source of direct voltage having its negative pole connected to the cathodes of said thermionic tubes, a potentiometer shunted across said source and having the arm thereof connected to the cathodes of said rectifier tubes, and vectorial addition means constituted by a load impedance connected in parallel to said anodes to produce an electrical oscillation having a phase angle substantially proportional to the amplitude of said modulating potential.

9. A phase modulation system comprising, means for generating a main electrical oscillation, phase shifting means coupled to said main oscillation generating means to derive from said main oscillation two partial oscillations of substantially equal amplitude and having a phase difference smaller than dr/Z radians, a source of a modulatin'g potential, two thermionic tubes each having a cathode, a first and a second control electrode and an anode, each of said first control electrode-s being connected to one of said phase shifting means, said second control electrodes being connected in push-pull to said source of modulating potential in a grid-current saturatiomcircuit arran'gement, and vectorial addition means consti tilted by a load impedance connected in pushpull to the anodes of said tubes to vectorially combine the non-linearly amplitude modulated otential oscillations and to produce an electrical oscillation having a phase angle substantially proportional to the amplitude of said modulating potential.

L. RUBIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,151,464 Curtis Mar. 21, 1939 2,165,229 Crosby July 11, 1939 2,220,201 Bliss Nov. 5, 1940 2,267,703 Henkler Dec. 23, 1941 2,301,907 Pie'raccl Nov. 10, 1942 2,318,934 Evans May 11, 1943 2,347,458 Brown Apr. 25, 1944 

